In drywall construction it is necessary, after taping and filling the joints between the panels, to sand the joint to reduce it to the same level as the adjacent panels and thus obscure any evidence of a joint.
In the past this had been done with manual sanders consisting simply of a supporting block and a section of abrasive material on the block. An improved power operated sander was disclosed in U.S. patent application Ser. No. 07/103 362, now U.S. Pat. No. 4,782,632, filed on Oct. 1, 1987, which is entitled "Drywall Sander" by Matechuk. In addition, U.S. patent application Ser. No. 07/901,694, now U.S. Pat. No. 5,239,783, filed on Jun. 22, 1992, which is entitled "Drywall Sander" by Matechuk, which was a continuation-in-part of the Matechuk '632 patent, describes certain improvements to the overall operation of the sander and some enhanced convenience features. In particular, refinements to the use of a vacuum hose were added. Also, an improved replacement procedure for the sanding surface was provided so that the operator no longer was required to remove a retaining bolt which held the sanding disc in place. Such a retaining bolt often times caused a delay in operating the sander when a screwdriver or other tools had to be found and used during the sanding surface replacement procedure.
Extraction of dust during operation of the sander is of great importance. The design of those areas in a sander through which the dust passes determines the continuing effectiveness of the extraction system as does the selection of the vacuum system.
Also, certain peculiarities to the sanding of drywall which may not be of the same importance in other sanding applications exist. The material used to cover the tape and fill the joint is easily abraded and care must be taken to avoid scoring the surface. The paper surface of the plaster board is also easily damaged when sanding. Selection of suitable characteristics of the abrasive material becomes of great importance. Also, the amount of force applied to the surface by the sanding pad and concentration of force on particular areas affects the final result.
The Matechuk '783 patent describes incorporating the vacuum line into the handle of the sander which eliminates the loose vacuum line adjacent the sanding head. Also, the shroud surrounding the sanding disc is contoured to provide a smooth, substantially constant, cross-sectioned duct for air flow from the sanding head into the handle and out to a vacuum system which is selected to handle the large quantities of dust produced during the sanding of drywall. Finally, to increase efficiency, the sanding disc is held on the drive plate by a quick release high compression locking device which permits rapid and positive replacement of worn abrasive discs.
The abrasive disc or pad used for sanding should be specially designed in view of the nature of the surface being sanded. One such abrasive pad is described in U.S. patent application Ser. No. 08/288,233, filed on Aug. 9, 1994, which is entitled "Abrasive Pad" by Chambers et al. In the case of drywall the abrasive pad should have a foam backing and should be faced with a grit of suitable size. Preferably the grit is coated directly on the foam but in any case the pad must retain its flexibility. The foam is selected to have a non-linear compression characteristic so that, when compressed, the force required to produce a given deflection increases as the foam is compressed. The foam also has what may be termed a quick memory; that is, when compressed and released the foam quickly recovers its original thickness.
Both the Matechuk '632 patent and the Matechuk '783 patent show and describe a pivot mechanism for the sanding head which only pivots the sanding head about a single axis. A user of a motorized sander typically needs to sand drywall surfaces on the walls and ceiling during a sanding session. In order to said several of these surfaces with a motorized sander that pivots about a single axis, the user needs to move about the sanding area and change positions frequently.
Therefore, a need exists for a mechanism which enables the sanding head to pivot through several axes of rotation so that the user does not need to change positions as frequently as is required when using other motorized sanders.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.